tv: add missing header for clock_gettime

Not sure how this symbol becomes visible in glibc (probably accidental
or mandatory recursive inclusion via the other standard or Linux-
specific headers), but normally this include file is needed to get the
symbol.

stream/tvi_v4l2.c

@@ -40,6 +40,7 @@ known issues:
 #include <pthread.h>
 #include <stdio.h>
 #include <string.h>
+#include <time.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>
 #include <sys/time.h>